Key-operating mechanisms for electronic musical instruments

ABSTRACT

In an electronic musical instrument having a plurality of keys which are selectively depressed to generate tone signals of predetermined pitches, each key is provided with a piezoelectric element for producing a pulsating signal having a voltage level varied directly with the depressive force applied upon the key and an electrical circuitry for controlling the volume and/or tone color of the reproduced musical sound in response to the voltage level of the pulsating signal.

United States Patent [72] inventor Takehiko Nagano l-lamamatsu, Japan [21] Appl. No. 84,955

[22] Filed Oct. 29, 1970 [45] Patented Jan. 11, 1972 [73] Assignee Nippon Gakki Seizo Kabushiki Kaisha Hamamatsu-shi, Japan [3 2] Priorities Oct. 31, 1969 [33] Japan Oct. 31, 1969, Japan, No. 44/103325; Oct. 31, 1969, Japan, No. 44/103326; Oct. 31, 1969, Japan, No. 44/103327; Oct. 31, 1969, Japan, No. 44/ 103328 [54] r KEY-OPERATING MECHANISMS FOR ELECTRONIC MUSICAL INSTRUMENTS 13 Claims, 12 Drawing Figs.

[52] US. Cl 84/1.01, 84/1.24, 84/1.26, 84/1.27 [5 1] Int. Cl G10c 3/12,

GlOh l/OO [50] Field of Search [56] References Cited UNITED STATES PATENTS 3,507.970 4/1970 Jones 84/l .26 X 3,564,105 2/l971 Amano..v 84/l .27 X

Primary Examiner-D. F. Duggan Assistant ExaminerUlysses Weldon Attorney- Kemon, Palmer & Estabrook ABSTRACT: In an electronic musical instrument having a plurality of keys which are selectively depressed to generate tone signals of predetermined pitches, each key is provided with a piezoelectric element for producing a pulsating signal having a voltage level varied directly with the depressive force applied upon the key and an electrical circuitry for controlling the volume and/or tone color of the reproduced musical sound in response to the voltage level of the pulsating signal,

PATENTEI] JAN! 1 I972 SHEET 1 [1F 3 FIG.

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SHEET 3 BF 3 1N VEXTOR KEY-OPERATING MECHANISMS FOR ELECTRONIC MUSICAL INSTRUMENTS BACKGROUND OF THE INVENTION This invention relates to a key-operating mechanism for an electronic musical instrument and more particularly to a novel key-operating mechanism wherein the volume and/or tone color of musical sounds generated by the selective operation of respective keys are varied utilizing piezoelectric elements for generating output pulses which vary in accordance with the depressive forces upon respective keys.

In such a keyboard musical instrument as, for example, a piano, it is not only possible to play musical sounds having tone pitches corresponding to selectively operated keys but also possible to vary the volumes of the musical sounds in accordance with the depressive forces upon the respective keys, thus providing the so called touch-responsive playing effect. However, in the conventional key-operating mechanism utilized in an electronic keyboard musical instrument such as an electronic organ, for example, the instrument is constructed such that tone signals having the desired pitches are generated from a tone generator by switching a key switch corresponding to the selectively operated key, so that such mechanism cannot provide the touch-responsive playing effect.

For this reason, with the key-operating mechanism of the conventional musical instrument, it is impossible to vary the tone volume or tone color of each note individually in accordance with the depressing force applied to the corresponding key.

SUMMARY OF THE INVENTION It is an object of the invention to provide an improved keyoperating mechanism for an electronic musical instrument which can provide the touch-responsive keying effect and variably control the volume and/or tone color of the musical sound in response to the depressive force applied on the key.

Another object of this invention is to provide a novel keyoperating mechanism which can induce an oscillation effect to the buildup portion of the musical sound.

According to this invention there is provided a key-operating mechanism for an electronic musical instrument having a plurality of keys which are selectively operated to generate tone signals of different tone pitches and piezoelectric elements, each for each key, each key including a mechanism for striking an associated piezoelectric element with a force varied directly with the depressive force applied thereon to produce a pulsating signal having a voltage level corresponding to the depressive force, a rectifier for rectifying the pulsating signal generated by the piezoelectric element and an electric circuitry to control the volume and/or tone color of the musical sound in response to the rectified pulsating signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view, partly in section, of one example of key-operating mechanism embodying the invention, for one key;

FIG. 2 is a block diagram of an electronic musical instrument utilizing the key-operating mechanism shown in FIG. 1;

FIG. 3 is a diagram of a keying circuit for one key;

FIG. 4 shows a diagram of at tone coloring filter for one key; and

FIGS. 5 to 12 inclusive show various other embodiments of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. 1 of the accompanying drawings, there is shown a keyboard musical instrument comprising a pluralityof juxtaposed keys 14 (only one of them is shown) which are arranged in the order of the musical notes one end of each key being pivotally mounted on a fulcrum 12 secured to a frame board 11 of the instrument. The key is normally maintained in substantially the horizontal position as shown by solid lines by means of a tension spring 13. When depressed, each key operates a corresponding key switch to cause a tone generator to produce a tone signal for pitch predetermined for the key.

According to this invention, following mechanism is incorporated with each key of the instrument. More particularly an L-shaped swinging arm 16 is provided to extend downwardly through a slot 10 of the frame board 11. The upper end of the arm 16 is pivoted to suitable fixed members (not shown) under the key 14 by means of a pine l5 and is normally biased rearwardly or toward the fulcrum 12 by means of a tension spring 17, the biasing force being counterbalanced by a stop weight 18. Thus the swinging arm 16 assumes a substantially vertical position when the key is not depressed. A roller 1950f rubber, plastic or metal is secured to the arm 16 by means of a pin 20 and a lever 21 which is substantially in parallel with the key 14.

roller 19, when the key is depressed, to the position as shown by a phantom. When driven by the key, the lower end portion of arm 16 is widely rocked forwardly as shown by a phantom against the force of the tension spring 20, the stroke and the speed of the forward movement of the arm being determined by the depressive force applied upon the key. A piezoelectric element 23 of Rossellesalt or barium titanate, for example, is disposed at a position to be struck by the arm 16 to generate a pulsating signal having a voltage level proportionalto the impulsive force across its terminals 24 and 25. The position at which the driving member 22 strikes the roller 20 is selected to be about one-half of the maximum depth of depression of the associated key. Thus, for example, when the fore end of the key is originally so designed as to be depressed to a depth of 9 to 10 mm., said striking is conducted at point about 4 to 5 mm. This arrangement ensures a large impacting force of the rod 22 for the roller 19 as well as quick response of musical sound for operation of the key.

Further, it is advantageous to leave a small gap S of about 1 to 2 mm. between the L-shaped top portion of the arm 16 and the piezoelectric element 23 when the key is depressed very slowly down to its lowest position. The small gap S allows the free and easy downward movement of the key 14 after the key has struck the piezoelectric element 23. The gap also provides a keying touch similar to that of a piano, that is, the force required for the depression of the key becomes suddenly small immediately after the arm 16 has struck the element 25. With this arrangement, only when the key is depressed with the depressive force beyond a certain limit the piezoelectric element 23 is struck by the L-shaped top portion of the arm 16 with an impactive force proportional to the depressive force applied upon the key, and thereafter the key can be depressed to its maximum depth with the driving rod 22 in engagement with roller 19.

FIG. 2 shows a block diagram of a musical instrument utilizing the key operating mechanism shown in FIG. 1. When one of the keys of a keyboard 31 is depressed, a keying circuit 32 corresponding to the depressed key is operated to pass a tone signal of a pitch corresponding to the depressed key from a tone generator 33. This tone signal is sent to a loudspeaker 36 successively through a tone-coloring filter 34, and an amplifier 35 to be reproduced as a desired musical sound.

According to this invention, the filtering characteristics and/or the volume control characteristics are varied in the following manner by the use of the piezoelectric element disposed as shown in FIG. 1 to produce a pulsating signal having a voltage level varied directly with the depressive force applied upon the key.

As shown in the diagram of FIG. 3 showing the keying circuit 32 corresponding to one key, one terminal 24a of the piezoelectric element 23a is grounded whereas the other terminal 25a is connected to the control electrode of an active element which operates as a type of a variable resistor, the

gate electrode of a field effect transistor FET,, for example, through a rectifier 41 comprising a diode D, of the polarity as shown in the drawing. The gate electrode of the transistor PET, is grounded though a capacitor C, and a series circuit connected in parallel with capacitor C, and including a resistor R, and a normal close key switch SW,. To the source (or drain) electrode of the transistor PET, is connected, through a capacitor C,,, an input signal source 42 which is connected to be derived a predetermined tone signal from the tone generator 33 when the corresponding key is depressed. The source (or drain) electrode is grounded through a resistor R,,. Further, the drain (or source) electrode of the transistor FET is connected to the input terminal of the amplifier 35 through a coupling capacitor C and is grounded through a resistor R Under the normal condition in which the key is not depressed, there is no signal applied to the source (or drain) electrode of the transistor FET, from the input signal source 42 and its gate signal is maintained at substantially zero potential Accordingly, under these conditions the transistor is set in its inoperative state manifesting highest impedance so that no output signal is derived out of its drain (or source) electrode. Upon depression of the key, however, the key switch SW, is opened and the input signal is supplied to the source (or drain) electrode of the transistor from input signal source 42. Concurrently therewith, a pulsating signal generated by the piezoelectric element 23a and having a voltage level varied directly with the depressive force upon the key is applied to the gate electrode of the transistor FET, through the rectifier 41. The rectified pulses also charge capacitor C,. Consequently, the transistor PET, is turned on to enable to supply the input signal from the source 42 to the loudspeaker 36 successively through the transistor FET,, coupling capacitor C and amplifier 35, thus producing a desired musical sound. The volume of the musical sound reproduced by loudspeaker 36 varies dependent upon the impedance exhibited by the transistor F ET,, which in turn varies dependent upon the rectified voltage for charging the capacitor C, having a voltage level varied directly with the depressive force upon the key. For this reason, the circuit arrangement including the piezoelectric element 23a, the rectifier 41 and the transistor FET, operates as a type of volume controller variably controlling the volume of the musical sound reproduced by loudspeaker 36. Upon release of the depressed key, the key switch SW, is reclosed to discharge capacitor C, through the resistor R,, thus turning off the transistor FET, to prepare for the next cycle.

FIG. 4 shows a diagram of one example of the tone-coloring filter 34 corresponding to one key. As shown, in order to vary the tone color of the musical sound to be reproduced by loudspeaker 36 in accordance with the depressive force applied to the key, the tone-coloring filter 34 having a construction to be described hereinbelow is connected between an input signal source 42 and the amplifier 35.

More particularly, one terminal 24b of the piezoelectric element 23b mounted as shown in FIG. 1 is grounded whereas the other output terminal 25b is connected to the control electrode of an active element which functions as a type of a variable resistor, for example, the gate electrode of a field effect transistor FET,, through a rectifier 51 comprising a diode D,, poled as shown. The gate electrode of the transistor is grounded through a capacitor C,, and a series circuit including a normal close key switch SW,, and a resistor R,, connected in parallel with the capacitor C,,. A resistor R is connected across the source and drain electrodes of the transistor FET,,. The source (or drain) electrode is grounded via a capacitor C whereas the drain (or source) electrode is connected between the input signal source 42 and amplifier 35. A coupling capacitor C,,, is connected between the input signal source 42 and the drain electrode of the transistor FET,, and, if desired, decoupling resistors R,,, and R,, may be connected as shown.

In operation, when the associated key is depressed, the piezoelectric element 23b produces a pulsating signal whose voltage level varies in response to the depressive force upon the key. This pulsating signal is rectified by the rectifier 51 to charge the capacitor C,,, whereby the impedance of the transistor FET,, is varied according to the terminal voltage of the capacitor C,,. In this manner, the transistor FET,, operates as a type of a variable resistor whose impedance varies directly with the depressive force upon the key. Thus the combined impedance of the transistor FET,, and resistor R, which are connected in parallel is decreased as the depressive force upon the key is increased. In this manner, the tone color of the tone signal generated by the tone generator 33 when a key of the keyboard is depressed is controlled by the tonecoloring filter 34 according to the depressive force on the key.

The change in the tone pitch provided by the tone-coloring filter is effected by varying the contents of the high-frequency components above the medium frequency band determined by the capacitance of the capacitor C,,. Thus, the quantity of the high-frequency components bypassed through the capacitor C increases with the depressive force on the key. Accordingly the tone color of the musical sound reproduced by loudspeaker 36 becomes rich in the low-frequency components as the depressive force is increased.

Although in FIG. 4, the transistor FET,,, resistor R,, and capacitor C are shown as connected in parallel relation between the input signal source 42 and amplifier 35, they may be connected in series with the signal source 42 and amplifier 35 in which case the tone color of the musical sound reproduced by loudspeaker will become rich in the highfrequency components as the depressive force is increased. It will be clear that the tone-coloring filter may be constructed to exhibit any desired tone color varying characteristic.

FIG. 5 shows a side view of a modified embodiment of the key-operating mechanism of this invention, wherein a leaf spring 62 including a weight 61 attached to the free end thereof is secured to the lower end of the swinging arm 16. In this construction when the arm 16 is caused to strike the piezoelectric element 23, the leaf spring 62 and weight 61 vibrate for a short interval with a decreasing amplitude, thus intermittently striking the piezoelectric element. As a result, the volume and/or tone color characteristics of the musical sound reproduced are varied complicatedly at the buildup portion, thus producing a delicate playing effect.

In another embodiment of this invention shown in FIG. 6, there is provided an inclined bracket 71 having its upper end secured to the lower surface of the frame board 11 at about the center of the key 14, and the lower end of a swinging arm 73 is pivotally connected to the lower end of the bracket 71. The upper end of the arm 73 extends through a slot 74 formed in the board 11 to rotatably support a roller 76 of rubber, plastic or metal. A driving member 78 having a downwardly and forwardly inclined portion 77 is fixed to the lower surface of the key at substantially the middle of its length. The arm 73 is biased forwardly or to the left as viewed in FIG. 6 by means of a spring 79 to cause the roller 76 to engage the lower surface of the inclined portion of the driving member 78 when the key is not depressed.

This modification operates in the same manner as the embodiment shown in FIG. 2 to strike the piezoelectric element 23 except that the driving member 78 is always in contact with the roller 76. However, it will be clear that the driving member 78 may be spaced a little from the roller 76 as in the case of the embodiment shown in FIG. 1 as to remove the effect of slight mistouch of the player on a key which should not be depressed at that time.

FIG. 7 shows a modification of FIG. 6 wherein an L-shaped leaf spring 81 carrying a weight 82 at its free end is secured to the swinging arm 73, the same effect being obtainable as in the embodiment shown in FIG. 5.

In the embodiment shown in FIG. 8, a pedestal 91 is secured to the upper surface of the board 11 at a point a little rear to the center of the key 14. An L-shaped swinging arm 94 comprising a rigid plate 92 and a leaf spring 93 is pivotally connected to the pedestal 91 by means of a pin 95. The leaf spring or leg 93 extends downwardly through an opening 96 perforated in the board 11 and a weight 97 is secured to the lower end of the leg 93 to cooperate with the piezoelectric element 23. The L-shaped swinging arm 94 is normally maintained in the balanced condition shown in the drawing with the rigid leg 92 lying horizontally. A driving member 98 is secured to the lower surface of the key 14 to strike the rigid arm 92 when the key is depressed. Utilization of the spring leg 93 permits the further depression of the key 14 after the weight 97 has struck the element 23 because of the deflection of the leaf spring 93, whereby it is possible to depress the key to its deepest position.

In still another embodiment of this invention shown in FIG. 9, the piezoelectric element 23 is mounted on the board 11 to face the center of the key 14 and a leaf spring 102 having a weight 101 at its free end is secured to the board 11 substantially in parallel with the key 14. A driving member 103 is secured to the lower surface of the key 14 to depress the leaf spring 102.

Upon depression of the key 14, the leaf spring 102 is depressed with the same force as the key depressing force to impact the piezoelectric element 23 with the weight 101. Similarly, the deflection of the leaf spring 102 permits the displacement of the key 14 to the deepest position after the weight 101 has hit the element 23.

FIG. shows a modification of the embodiment shown in FIG. 9 wherein the free end of a leaf spring 113 carrying a weight 112 is anchored by an L-shaped catch or driving member 111 secured to the lower surface of the key 14. Since the leaf spring 113 is normally biased downwardly by the weight 112, when the key is depressed, the weight 112 is caused to strike the piezoelectric element 23 with a strength corresponding to the depressive force applied to the key, thus enabling more light touch of the key than the embodiment shown in FIG. 9. The element 23 is disposed halfway between the highest and lowest rocking positions of the key 14 so that the element 23 is hit by the weight 112 before the depressed key reaches the lowest rocking position.

In the embodiment of this invention shown in FIG. 11 a driving member 121 of soft rubber or plastic is secured to the lower surface of the key 14 substantially at its center and a damper 122 of similar material is secured to the upper surface of the board 11 to face the driving member. The piezoelectric element 23 is secured to the free end ofa leaf spring 123 to be positioned between the driving member 121 and damper 122, the other end of the leaf spring 123 being secured to the board 11 through a conductive lead 124. The other output lead 125 extends through the damper 122 and board 11. In this modification when the key 14 is depressed the piezoelectric element 23 is struck by the driving member 121 and compressed between the driving member 121 and damper 122 to generate a pulsating signal having a voltage level proportional to the depressive force of the key. By the vibratory action of the leaf spring, the piezoelectric element is struck several times to generate several pulses, thus improving the playing effect.

In still another modification of this invention shown in FIG. 12, the piezoelectric element 23 is secured on the top of a plunger 138 movable in a sleeve 132 extending upwardly through the board 11. A casing 135 is secured to the sleeve 132 and a compression spring 131 is interposed between a flange 137 of the plunger 138 and the bottom of the casing 135. An annular cushion 136 of felt, for example, is disposed between the flange 137 and the top of the casing 135. Accordingly, when the key 14 is depressed the piezoelectric element 23 is moved downwardly against the force of the compression spring 131.

According to this invention, the piezoelectric element is struck by the key halfway between the normal or highest rocking position of the key and the lowest rocking position thereof, that is to say, the musical tone is produced before the key reaches the lowest rocking position, and accordingly the key-operating mechanism of this invention gives the player no What is claimed is: I

l. A key-operating mechanism for an electronic musicalinstrument having a plurality of keys which are selectively operated to generate tone signals of different tone pitches and piezoelectric elements each for each key, each key including a mechanism for striking the associated piezoelectric element with a force corresponding to the depressive force applied thereon to produce a pulsating signal having a voltage level varied directly with the depressive force, a rectifier for rectifying the pulsating signal generated by said piezoelectric element and an electric circuitry to control at least one of the volume and tone color of the reproduced musical sound in accordance with the rectified pulsating signal. j

2. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a swinging arm pivotally mounted under said key, a spring to urge said swinging arm to a position remote from said piezoelectric element, and means to drive said swinging arm to strike said piezoelectric element with a force corresponding to the depressive force applied upon said key.

3. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a substantially L- shaped swinging member including a rigid member and a leaf spring which are interconnected into said L-shape means to pivotally mount said L-shaped swinging member under said key, a weight secured to said leaf spring to hold said rigid member substantially in parallel relation with said key, and means for driving said swinging member with a force proportional to the depressive force applied to said key thus causing said weight to strike said piezoelectric element.

4. The key-operating mechanism according to claim 1 wherein said swinging arm comprises a leaf spring fixed at one end to extend substantially in parallel with said key, a weight secured to the free end of said leaf spring and means to deflect downwardly said leaf spring when said key is depressed thus causing said weight to strike said piezoelectric element with a force corresponding to the depressive force applied to said key.

5. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a catch secured to said key, a leaf spring with one end fixed and the other end caught by said catch, and a weigh secured to said leaf spring at a point intermediate the ends thereof whereby when said key is depressed said weight is caused to strike said piezoelectric element by the flexure of said leaf spring with a force corresponding to the depressive force applied to said key.

6. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a driving member secured to the lower side of said key, a stationary cushion confronting said driving member, a leaf spring with one end fixed and a piezoelectric element secured to said leaf spring between said driving member and said cushion whereby said piezoelectric element is struck by said driving member with a force proportional to the depressive force applied to said key.

7. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a driving member secured to the lower surface of said key, a plunger located under said driving member for supporting said piezoelectric element and compression spring urging said plunger toward said driving member.

8. The key-operating mechanism according to claim 1 wherein said electric circuitry comprises a rectifier for rectifying said pulse signal generated by said piezoelectric element, a capacitor charged by the output from said rectifier, a variable resistance element whose resistance is'varied in accordance with the terminal voltage of said capacitor, and an amplifier to amplify the tone signal generated when said key is operated and passed through said variable resistance element so as to vary the volume of said tone signal in accordance with the depressive force applied to said key.

9. The key-operating mechanism according to claim 1 wherein said electric circuitry comprises a rectifier for rectifying said pulse signal generated by said piezoelectric element, a capacitor charged by the output from said rectifier, and a 12. The key-operating mechanism according to claim 2 wherein said swinging arm includes a roller driven by said key when the key is depressed.

13. The key-operating mechanism according to claim 2 wherein the lower end of said swinging arm is pivotally connected to a supporting arm. a roller is mounted on the upper end of said swinging arm, and said roller is normally urged against said driving means by means of a spring whereby when said key is operated said roller is caused to strike said piezoelectric element with a force proportional to the depressive force applied on said key. 

1. A key-operating mechanism for an electronic musical instrument having a plurality of keys which are selectively operated to generate tone signals of different tone pitches and piezoelectric elements each for each key, each key including a mechanism for striking the associated piezoelectric element with a force corresponding to the depressive force applied thereon to produce a pulsating signal having a voltage level varied directly with the depressive force, a rectifier for rectifying the pulsating signal generated by said piezoelectric element and an electric circuitry to control at least one of the volume and tone color of the reproduced musical sound in accordance with the rectified pulsating signal.
 2. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a swinging arm pivotally mounted under said key, a spring to urge said swinging arm to a position remote from said piezoelectric element, and means to drive said swinging arm to strike said piezoelectric element with a force corresponding to the depressive force applied upon said key.
 3. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a substantially L-shaped swinging member including a rigid member and a leaf spring which are interconnected into said L-shape means to pivotally mount said L-shaped swinging member under said key, a weight secured to said leaf spring to hold said rigid member substantially in parallel relation with said key, and means for driving said swInging member with a force proportional to the depressive force applied to said key thus causing said weight to strike said piezoelectric element.
 4. The key-operating mechanism according to claim 1 wherein said swinging arm comprises a leaf spring fixed at one end to extend substantially in parallel with said key, a weight secured to the free end of said leaf spring and means to deflect downwardly said leaf spring when said key is depressed thus causing said weight to strike said piezoelectric element with a force corresponding to the depressive force applied to said key.
 5. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a catch secured to said key, a leaf spring with one end fixed and the other end caught by said catch, and a weigh secured to said leaf spring at a point intermediate the ends thereof whereby when said key is depressed said weight is caused to strike said piezoelectric element by the flexure of said leaf spring with a force corresponding to the depressive force applied to said key.
 6. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a driving member secured to the lower side of said key, a stationary cushion confronting said driving member, a leaf spring with one end fixed and a piezoelectric element secured to said leaf spring between said driving member and said cushion whereby said piezoelectric element is struck by said driving member with a force proportional to the depressive force applied to said key.
 7. The key-operating mechanism according to claim 1 wherein said striking mechanism comprises a driving member secured to the lower surface of said key, a plunger located under said driving member for supporting said piezoelectric element and compression spring urging said plunger toward said driving member.
 8. The key-operating mechanism according to claim 1 wherein said electric circuitry comprises a rectifier for rectifying said pulse signal generated by said piezoelectric element, a capacitor charged by the output from said rectifier, a variable resistance element whose resistance is varied in accordance with the terminal voltage of said capacitor, and an amplifier to amplify the tone signal generated when said key is operated and passed through said variable resistance element so as to vary the volume of said tone signal in accordance with the depressive force applied to said key.
 9. The key-operating mechanism according to claim 1 wherein said electric circuitry comprises a rectifier for rectifying said pulse signal generated by said piezoelectric element, a capacitor charged by the output from said rectifier, and a tone-coloring filter including a variable resistance element whose resistance is varied in accordance with the terminal voltage of said capacitor whereby to control the tone color of the tone signal generated by the depression of said key in accordance with the resistance variation of said resistance element.
 10. The key-operating mechanism according to claim 8 wherein said variable resistance element is an active circuit element.
 11. The key-operating element according to claim 9 wherein said variable resistance element included in said tone-coloring filter is an active circuit element.
 12. The key-operating mechanism according to claim 2 wherein said swinging arm includes a roller driven by said key when the key is depressed.
 13. The key-operating mechanism according to claim 2 wherein the lower end of said swinging arm is pivotally connected to a supporting arm, a roller is mounted on the upper end of said swinging arm, and said roller is normally urged against said driving means by means of a spring whereby when said key is operated said roller is caused to strike said piezoelectric element with a force proportional to the depressive force applied on said key. 